1. Field of the Invention
This invention pertains generally to remote control of irrigation valves, and more particularly to an apparatus for permitting multiple solenoid operated irrigation valves to be controlled from a single control line from an irrigation controller.
2. Description of the Background Art
Landscape sprinkler systems are inherently inflexible. Water is supplied through a pipe which limits its volume so strategically placed valves are used to divide the water among many landscaped areas. Automatic control of these valves is usually electrical which requires a control wire for each valve and a common return wire to all valves. Once an automatic sprinkler system is installed it is both difficult and expensive to increase the number of control wires.
A drop in water pressure requires more valves to further divide the sprinkler systems and a broken wire in an inaccessible place necessitates a major expense to reroute it. Land use changes such as new buildings, parking lots and roadways often require more valves than did the previous large uninterrupted landscape.
In attempting to add some flexibility to this rigid system in a practical way, many devices have been proposed. For example, U.S. Pat. No. 4,985,638 to Brock, which is incorporated herein by reference, and U.S. Pat. No. 4,575,004 to Geiger, which is also incorporated herein by reference, attest to the importance of such devices, but deficiencies still remain. One such deficiency is that devices such as shown in U.S. Pat. No. 4,575,004 require continuous power, as do all of the competing products. The requirement of continuous power makes such units unsuitable for use with certain controllers. For example, some controllers, such as the Irritrol IBOC, are battery powered for use where there is no electric utility available such as highway overpasses, traffic islands and isolated parks. An irrigation system designed for the Irritrol IBOC cannot use standard controllers or valve solenoids because of the unique way the system operates. To conserve batteries, the Irritrol IBOC valve solenoids are latched magnetically by a short, polarized electric pulse from the controller. An 18-volt DC pulse sent through the field circuit in one direction for 20 ms will open a valve. At the end of the programmed watering time, a 24 volt DC pulse sent through the same circuit for 20 ms in the opposite direction will close the valve.
New control technology has added new problems too, such as "self diagnostic" circuits in the central controller which shuts down individual field circuits rather than the entire controller. The development of very low power valve actuators has invited controller manufacturers to develop complex electronic designs as well as very inexpensive residential controllers. This further tightens the parameters of any device inserted into the field circuitry.
Therefore, there is a need for a valve controller expansion apparatus that is compatible with the various controllers commercially available, including those which operate on battery power. The present invention satisfies the needs of the industry and overcomes the deficiencies in conventional control systems in a way that is novel and nonobvious.